I use an odyssea twin tube T5HO fluorescent over my 29g with plants. This fixture would fit 20long, 29 and 37g tanks (well.. anything 30" wide) Fixture is ~48watts total.
TBear, the problem with fluorescent plant lighting is, even though the bulbs look good to the eye, they have to be swapped out every 6-12months if you want them to keep growing plants. Their output intensity fades with use.
Again.. why say it once when you can say it 3-4x in one thread.. You might want to concentrate on water parameters and establishing an environment your fish can continue to live in first, then move on to plants, which can help the tank environment thing..